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Management in multiple effect evaporator system: A heat balance analysis approach
Abstract
With the increase in awareness to cost curtailment of energy consumption coupled with the increase in the consumption of the concentrated and dehydrated food products, energy management has become indispensable in food industries. One such process of obtaining these food products is by employing evaporation in food industries. The process of evaporation is employed in the food industry primarily as a means of bulk and weight reduction for fluids. Therefore, evaporation is one of the most large scale operations in food industry. Energy is the most important running cost item in evaporation. High energy consumption is known to have direct or indirect impact on climate change. The operating cost of an evaporator system is mostly determined by the energy that is required to achieve certain evaporation rate. Under steady state condition there must be a balance between the energy entering and leaving the system. Energy can be saved by re-using vapour formed from the boiling product. One of the few ways of accomplishing such is by multiple-effect evaporation. This paper is attempted to explain how total cost of evaporation can be reduced by using multi-effect evaporator thereby achieving an economically optimal number of effects. This can be proved through application of heat-balance analysis.
... Evaporators, precisely multi-effect evaporators, have become an integral part of many processes in wide industries including sugar, paper and pulp, dairy, desalination, food processing and pharmaceuticals, etc. (Shah & Bhagchandanc 2012, Sarma & Barma 2010, Kumar et al. 2013, Kumar et al. 2010, Zain & Kumar 1996, Danish & Sachin Pratap 2014, Bhargava et al. 2008. Multi-effect evaporators yield high value of the coefficient of performance in comparison to a single effect evaporator system. ...
Pharmaceutical effluent disposal is a serious problem in the present times. The manufacturing process involves the use of both organic and inorganic compounds, which contribute to high chemical oxygen demand and dissolved solids. The common techniques used to extract available salts and to produce reusable waters are evaporation and cooling. Evaporators are equipment used for evaporation which is a kind of heat transfer system in which transfer mechanism is controlled by natural or forced convection. Multi-effect evaporators in many industries are used for volume reduction and cutting down the waste handling cost. This paper focusses on studying the efficiency of multi-effect evaporators in the pharmaceutical industry for the treatment of high total dissolved solids (HTDS) waste streams. The feed and condensate parameters were monitored for three years. Competence of the treatment process is presented in terms of reduction in TDS and COD. The current study evaluates the efficiency of MEE in terms of removal of total dissolved solids and chemical oxygen demand. Removal efficiencies are more than 98% for TDS and 50% for COD.
... Normally, all effects in an evaporator will be physically the same in terms of size, construction, and heat transfer area. [5] Unless thermal losses are significant, they will all have the same capacity as well. ...
The effects of heat transfer performance of systems can be studied in combination with thermodynamic performance. The design solution of maximizing heat transfer always leads to increased entropy generation else if minimizing entropy was aimed then heat transfer got minimized. Hence there is need for holistic optimization. This paper attempts to merge the two competing criteria’s - (i) heat transfer and (ii) the thermodynamic performance of a solar assisted multiple effect evaporator system and optimize study parameters for its energy efficient operation. Solar assisted multiple effect evaporators use steam as source of energy to evaporate wastewater.
The idea of amalgamating these two factors is to observe how much reduction in the performance of one factor will improve the performance of the other. This study couples the two criteria, which has been dealt with separately, to arrive at the parameters of interest which must be fine-tuned for ensuring system performance.
Mass flow rate of steam and wastewater appeared to chiefly influence heat transfer and entropy generation of the system, negligible influence was observed on changing the concentration of the waste water or optical efficiency of the solar concentrator in single legged analysis. However through this holistic optimization study, it was found that variations in Prandtl number, i.e., the concentration of the waste water and optical efficiency of solar concentrator drastically shift the optimization balance of entropy generation and heat transfer rate.
... Energy can be saved by reusing vapor formed from the boiling product. One of the few ways of accomplishing such is by multiple-effect evaporation, [6]. ...
The most important running cost item in evaporation is energy. However, energy consumption per unit production can be reduced considerably through the use of multi effect evaporation. A multiple effect evaporation scheme was studied and economically analyzed. Different economic items, including cost of steam and cost of evaporator in addition to annual total cost for single, double, three, four, five and six effects of evaporators were estimated and analyzed. The results indicated that minimum annual total cost is obtained by using a double effect evaporator.
... The main parameters of the MED unit, which have appreciable effects on the performance of the desalination plant, are the dimensions of each effect and the total number of effects [30][31][32]. However, the main design target of a desalination plant is to achieve minimum heat loss, while using the minimum power required for the plant. ...
In the present work, theoretical investigation of the performance of two sequential desalination systems, multi-effect distillation and mechanical vapor compression, is carried out. A mathematical model is developed and implemented in MATLAB and validated by results available in the literature. Then the parametric analysis is carried out to produce distillate water and salt utilizing renewable energy. A parametric analysis has been conducted to understand the important factors that affect the performance of the plant. Furthermore, three sites are selected in Egypt (Marsa Matrouh, Ras Benas, and Taba) and economic feasibility of the proposed desalination system is carried out and compared with plant economy of conventional fossil fuels. The results show that site location, solar intensity, wind speed, ambient temperature, and water salinity are the most dominant factors in the performance.
... With the increase in awareness to cost curtailment of energy consumption coupled with the increase in the con- sumption of the concentrated and dehydrated food prod- ucts, energy management has become indispensable in food industries. Energy is the most important running cost item in evaporation (Gunajit and Surajit 2010). ...
Evaporation is commonly used by various processing industries as a method of concentrating aqueous liquid streams by vaporizing the water component. The comparison of two schemes of evaporation was studied and economically analyzed. Recompression evaporation could be defined as an evaporation process in which a part or the entire evaporated vapor is compressed by means of a suitable compressor to a higher pressure level and then condensed. Two recompression schemes were studied: (1) mechanical compression; and (2) thermal compression. Different economic items, including cost of steam, electricity, fixed cost of compressor and cost of evaporator, in addition to annual total cost for each scheme have been estimated and analyzed. The results indicated that minimum annual total cost is obtained by using a steam jet ejector scheme.
It is essential that evaporation be approached from the viewpoint of economical energy utilization as well as process effectiveness. This can be done only if the equipment manufacturer is able to offer a full selection of evaporation technology and systems developed to accommodate various product characteristics, the percent of concentration required and regional energy costs.
The food industry is one of the most suitable sectors for solar process heat applications. Concentrating solar power (CSP) systems generate steam using mirrors or lenses to concentrate a large area of sunlight onto a receiver. In this study, how a CSP system connected hybrid to the boiler system can be utilized to produce more sustainable peach puree concentrate (PPC) have been examined. The amount of steam required for PPC production was calculated using the measurements rendered in a real fruit juice concentrate plant and the data obtained from them. A parabolic trough‐type CSP system of 1 MWth was designed, which is placed in the area of the plant, and it was determined that the steam quantity obtained during the production period is able to meet how much of the current consumption. Also, it has been shown how much CO2eq emission reduction will be achieved by using CSP.
Practical Applications
Concentrated fruit juice production is one of the thermal energy intense food processes. Therefore, utilization of renewable energy sources for process heat is very important. We designed a CSP system in this study with using production data from a real fruit juice factory. This CSP system is naturally applicable to both fruit juice and all food industry using steam at similar temperatures and pressures. Fossil fuels are one of the main responsible for global warming. For this reason, the use of solar thermal systems is promising to ensure sustainability in food production and reduce the environmental impacts of the product.
Multiple effect evaporators (MEE) use steam of temperature 120–200 °C for evaporation of water. Conventionally, the steam fed to MEE is generated by conventional fuel-fired boilers, in the current study concentrated solar energy is employed as an alternative. A system model was designed to study the temperature of steam generated on an hourly basis throughout the year and its exergy performance in different climatic zones of India. Except winter months and monsoon days, the solar concentrator generated the desired temperature of steam, thereby was not affecting the performance of the multiple effect evaporator system. Auxiliary support will be necessary during such durations to raise the steam temperature from 70 °C to the desired range. An hourly variation in solar radiation does not significantly affect the performance of the solar-assisted MEE system. Influence of the system performance on varying parameters has also been studied using the model. Reynolds number (Re) of the wastewater flow was found chiefly influencing the energy and exergy performance of the device, the change in Re can cause up to 60% variation in exergy and energy of the system.
Evaporasi merupakan proses penghilangan sebagian besar air pada bahan dengan cara memberikan panas pada titik didihnya menggunakan evaporator. Proses evaporasi menghasilkan uap air yang dapat dimanfaatkan untuk pembangkitan proses serupa. evaporator double effect termodifikasi merupakan alat evaporasi dengan proses penguapan berganda dan bekerja pada tekanan dibawah 1 atm. Energi uap yang dihasilkan dari penguapan bahan di ruang proses 1 (efek 1) akan digunakan untuk pemanasan bahan di efek 2. Tujuan penelitian adalah melakukan pengujian pada aspek teknis terutama efisiensi energi dari mesin evaporator double effect termodifikasi pada bahan nira tebu. Pengukuran dan pengamatan pada proses evaporasi dilakukan terhadap data suhu bahan dan uap, tekanan vakum, volume bahan, konsumsi bahan bakar, rendemen giling sementara batang tebu, dan pengurangan volume bahan. Pencatatan suhu, tekanan, dan volume dilakukan setiap 10 menit. Hasil pengamatan suhu titik didih bahan didapatkan sebesar 63,4 oC pada tekanan rata-rata sebesar -60 CmHg. Pengamatan konsumsi bahan bakar menunjukkan bahwa pada 5 jam 20 menit proses rata-rata sebesar 21.312 kJ/jam. Pada efek 1 rata-rata presentase pengurangan kadar air sebesar 54% sedangkan pada efek 2 sebesar 20,7%. Didapatkan nilai efisiensi rata-rata sebesar 56,3%.
The evaporation of water from an aqueous solution is widely used in the food, desalination, pulp, and chemical industries. Usually, a large amount of energy is consumed in the evaporation process to boil off water due to atmospheric pressure. As a way of improving the energy efficiency of the evaporation process, the combination of multiple effect evaporation and thermal vapor recompression has been proposed and has become a successful technique. In this study, 4 multiple-effect falling film type evaporators for sugar solution are designed and the energy efficiency of the system is analyzed in response to the selection of the steam ejector position. Energy efficiency is increased and vapor is more compressed in the steam ejector as the Thermal Vapor Recompression (TVR) is arranged in the rear part of the evaporator system. A simplified 0-dimensional evaporator model is developed using non-linear equations derived from mass balances, energy balances, and heat transfer equations. Steam economy is calculated to compare the evaporation performance of the 4 proposed evaporators. The entrainment ratio, compression ratio, and expansion ratio are computed to check the ejector performance.
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